In recent years, high-pressure treatment has started to be utilized as a method for, among other things, inactivating microorganisms (e.g. bacteria) in foodstuffs, especially foodstuffs such as fruit juices and the like which have a particularly high quality. The advantage of high-pressure treatment as compared with the more frequently used heat-treatment method is that the microorganisms in the freshly pressed juice are inactivated without destroying vitamins and flavouring, which occurs during heat treatment and which requires additives in the heat-treated juice to restore, as tier as possible, the nutritive value and taste of the freshly pressed juice.
During high-pressure treatment of foodstuffs, it is desirable that the surfaces in the pressure chamber, with which the foodstuff may come into contact, be made of a material which is inert in relation to the foodstuff. An example of such a material is stainless steel. The problem with stainless steel, however, is that its strength is considerably lower than the strength of the high-strength, non-stainless steels from which pressure vessels for high pressures are normally manufactured. This means, among other things, that an upper limit to the pressure, to which foodstuffs have hitherto been capable of being subjected for the above-mentioned purpose, has been at around 4000 bar. Pressures of this order of magnitude are sufficient to inactivate microorganisms, but not to inactivate enzymes, which, for example, as far as fruit juices are concerned, contribute to separate the juice. Nor are these pressures sufficient to inactivate spores.